This invention relates to the use of a heat-activatable sealing piston in thermal actuators and in particular it relates to the use of such a piston in an electrical connector.
In U.S. patent application Ser. No. 483,997, filed Apr. 11, 1983, there is disclosed an electrically conductive connector for electrical conductors. In some embodiments, a solid slug of solder is positioned in the base of the connector and a conductor is then inserted. When sufficient heat is applied to melt the solder, a pressuring means forces the solder between the conductor and the side walls of the connector and, if a stranded conductor is used, between the strands of the conductor. A preferred pressuring means comprises a piston and a composition which on application of heat evolves a gas. On continued heating, the solder melts and the pressure of the evolved gas acts on the piston causing it to move toward the open end of the connector and force the solder between the conductor and connector. A problem encountered with this embodiment is the difficulty of providing a seal around the piston to prevent leakage of the gas or the gas evolving substance before sufficient pressure has been developed.
This invention provides a sealing piston which can be used in such a connector. Further, the sealing piston is capable of use in other systems or apparatus such as thermal actuators which operate, for example, a relief valve. This invention provides a heat activatable sealing piston which, when positioned within a tube and heated, expands and provides a seal between the piston and the walls of the tube which on application of pressure is capable of axial motion within the tube while maintaining the seal.
Heat expandable devices are known. For example, heat expandable rivets and the like have been proposed in the art. See for example Swiss Patent No. 423,209 to Dynamit Nobel and U.S. Pat. No. 2,458,152 to Eakins. The heat expandable rivets described in these patents are used to securely fasten one object to another. Movement of the rivet after installation is not possible nor is it desirable.
U.S. Pat. No. 3,243,211, to Wetmore, mentions the use of heat expandable tubular articles. The use of such articles closed at one end can be used to plug, for example, pipes or other conduits. In accordance with the Wetmore invention, a fusible member, such as an adhesive, is positioned on the expandable article. On application of heat, the fusible member melts and flows. As a result, the plug is securely bonded to the inner walls of the pipe.
The use of a sealing piston in thermal actuators is described in U.S. Pat. No. 3,302,391, to Mihm. In this patent an elastomeric plug is used as a sealing piston within a tube. To effect the seal, washers are provided at each end of the plug and a screw, which extends through the plug and washers, can be tightened to cause the plug to expand radially and thereby form a seal between the plug and the walls of the tube. The plug is positioned within the tube on top of a column of heat expandable material, such as wax which expands on melting. When heated the material melts and expands and, since it is confined by the walls of the tube, the expansion is in the axial direction. The elastomeric plug is subjected to an axial force which produces an increase in the radial pressure exerted by the plug on the walls of the tube and causes the plug to move longitudinally in the tube thereby operating a relief valve to which it is connected. The assembly can be used, for example, in a hot water tank. Similar devices are disclosed in U.S. Pat. Nos. 3,194,009 to Baker and 3,319,467 to Feinberg.